Fluorescence light microscopy is extensively used in biological research and medical diagnosis. It provides the selectivity necessary to enable specific components of a cell or tissue to be visualized and the spatial organization of such components to be determined. A major problem of the technique is that light emission from out-of-focus regions seriously degrades the signal-to-noise ratio of the image, especially when thick objects are viewed. Confocal microscopy addresses and to a large extent solves this problem. In a confocal microscope, both illumination and detection are confined to a single point in the sample. This is achieved typically by using spatial filters (usually pinholes) in the optical paths of the objective and condenser. A complete image is built up by sequentially scanning all points in the field of view.